1. Field of the Invention
The present invention relates to an insulator which exhibits a high thermal conductivity, and a method for producing the same. The insulator exhibiting a high thermal conductivity in accordance with the present invention can be used as a heat radiating board, a heat sink, an electromagnetic wave shielding material exhibiting heat radiating properties, too, etc., which have been assembled in various electrical equipments.
2. Description of the Related Art
As electronic parts have been packed with a higher density and hybrid powered vehicles have been increased, the development of heat radiating properties of various electrical equipments has been demanded. For example, in order to accelerate the cooling of CPU, a metallic heat sink exhibiting a high thermal conductivity has been placed on the CPU, and cooled with air by means of fans. However, heat radiating boards, etc. used in the electrical equipments are frequently required to exhibit electrical insulating properties, too, and it is generally difficult that the thermal conductivity and the electrical insulating properties are both exhibited.
Under the above-described circumstances, it has been considered to use heat radiating boards composed of insulating resins, because by mixing materials, each exhibiting a high thermal conductivity, into the resins, the resultant heat radiating boards can exhibit satisfactory thermal conductivity and electrical insulating properties. Ceramics, ex. exhibit a comparatively high coefficient of thermal conductivity, and excellent insulating properties. Therefore, it can be considered to use molded bodies which are composed of the resins mixed with ceramics powder as the heat radiating boards.
In the molded body composed of a resin matrix in which ceramics powder is dispersed, however, thermal conductivity is exhibited due to accidental continuities of the ceramics powder so that in order to obtain an objective thermal conductivity, the content of the ceramics powder must be increased. However, as the content of the ceramics powder increases, the molded body may become brittle, or the molding thereof may become difficult due to the brittleness of ceramics itself. In addition, production costs become expensive.
Publication of unexamined Japanese patent application No. 2000-281802 discloses a thermal conduction molded body which is prepared by applying a magnetic field to a molding material composed of a resin and a diamagnetic material powder, orienting the diamagnetic material powder in a prescribed direction and solidifying the molding material. When the magnetic field is applied to the diamagnetic material powder, the diamagnetic material powder is oriented in the directions along the lines of magnetic force so that even a small amount of the diamagnetic material powder serves to exhibit continuity, and consequently exhibit a high thermal conductivity. Accordingly, the content of the diamagnetic material powder can be reduced while maintaining the thermal conductivity.
The thermal conduction molded body disclosed in the above publication, however, was insufficient in heat radiating properties, because such the thermal conduction molded body is composed of the resin and the diamagnetic material powder. In addition, the thermal conduction molded body disclosed in the above publication has the characteristics that the heat radiating properties in the direction vertical to the orienting direction are low, and consequently, the anisotropy in heat radiating properties is big. However, the anisotropy in heat radiating properties of the thermal conduction molded body disclosed in the above publication is insufficient. Accordingly, further improvement of the anisotropy in heat radiating properties is needed.